1. Field of the Invention
The present invention relates to an instant film unit of a self-developing type.
2. Description Related to the Prior Art
An instant film unit (hereinafter referred to as a “film unit”) has a peel-apart type and a monosheet type. Each of them maintains a characteristic of providing a printed photo soon after photography. In the peel-apart type, after the film unit is loaded into a printer or an instant camera and is recorded an image, a photosensitive sheet is overlaid on an image receiving sheet by an operation of pulling a tab. The peel-apart film unit needs a manual step of putting those overlaid sheets into between a spreading roller pair. On the other hand, the film unit of the monosheet type is in a sheet shape, and it is possible to eject the film unit outside automatically. Therefore, the monosheet film unit is widespread among the general public.
A printer using the film unit is assembled such that an exposure head in a line shape is moved on the photosensitive surface of the film unit and exposes three fields of red, green and blue sequentially, then the exposed film unit is ejected through the spreading roller pair while it is processed (JP-A 2002-023254).
The monosheet film unit includes a photosensitive surface on which a latent image is created by exposure, a photosensitive sheet having a image creating surface on which a positive image is created, a cover sheet overlaid on the photosensitive sheet, a developing solution pod for containing developing solution to be spread between these sheets, a trapping material for catching a surplus of the developing solution being spread. Furthermore, these components are integrated by a white mask sheet (U.S. Pat. No. 6,304,725).
The film unit described in U.S. Pat. No. 6,304,725 has the approximately same size as a business card or a credit card(hereinafter referred to as a card size). The film unit has such a size to fit into a widespread business card holder (54 mm width×86 mm length) that it may be easy to arrange a plurality of the exposed film units (photo prints). Moreover, by filing a plurality of the business card holders containing the photo prints, it is possible to make a photo album readily and to watch well-organized photo prints.
In the film unit described in U.S. Pat. No. 6,304,725, a photosensitive layer and a image receiving layer are formed on each face of one sheet. Accordingly, an exposing side is different from an observing side. The film unit described in U.S. Pat. No. 4,639,963 includes a transparent image receiving sheet and a photosensitive sheet. The exposing side is the same as the observing side. In either film unit, a positive image is in a rectangle. Further, for the purpose of providing a more decorative effect, there are the known instant films. One of which is pre-exposed a frame on the inside margin of the opening on the mask sheet (JP-U 63-73743), and another includes the opening for the exposure in a heart shape or a circle (JP-U 3048920).
However, the developing solution pod and the portion including the developing solution pod becomes thick to some extent, because the film unit generally includes a developing solution pod containing developing solution with a certain extent of extra, for spreading the developing solution on the whole exposure area. Also, due to an increased surplus of developing solution, a trapping material to be used for catching the surplus has necessarily to have a certain thickness, and the portion including the trapping material also becomes thick. Thus, when the film unit has a thickness, there is a problem that it is bulky in the card folder or the album.